Whether for primary or revision arthroplasty, cutting guides are typically employed to ensure that any required resections correspond to mating surfaces of the prosthetic component. In knee replacement surgery, for example, a rod is typically inserted into the medullary canal of the proximal tibia, and a cutting guide is temporarily secured to this rod. Such guides include one or more slots into which the blade of an oscillating saw is inserted from anterior to posterior to shape the end of the bone in accordance with corresponding surfaces of the prosthetic element.
Extramedullary guide systems are also familiar to the art and typically provide a means for alignment and securing a cutting block on the proximal tibia.
In the case of a revision, the procedure is usually more elaborate due to deterioration of the previously prepared surfaces resulting from decomposition of the bone/prosthesis interface, necrosis, osteolysis, and other factors. Cutting blocks used in revision procedures therefore include slots corresponding to augments used to fill gaps between major resections and the mating surfaces of the prosthetic component. In the case of proximal tibial repair, such augments are typically wedge-shaped to account for proximal loss. Although more recently introduced techniques attempt to base the cuts on an intramedullary guide to which additional cutting blocks are mounted, there remains an unacceptable margin of error, the correction of which in some cases requires a freehand shaping of the bone. In addition, lateral defects require reshaping without injury to the patellar tendon which obstructs a saw blade when approached from the front of the knee.